Reagent addition system and method

ABSTRACT

A piston coupling for a micro-liter range liquid dispensing system for connecting a piston to a piston drive shaft generally includes a U-shaped body portion having a U-shaped arm and an annular barrel-shaped bearing seated in the U-shaped body portion and retained by the U-shaped arm. The bearing includes an axial bore for receiving the piston, wherein the annular barrel-shaped bearing is designed for balancing the forces applied to the piston by the piston drive shaft symmetrically about the centerline of the piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/132,366, filed on Apr. 25, 2002, now U.S. Pat. No. 7,125,520 whichclaims the benefit of U.S. Provisional Application No. 60/286,388, filedon Apr. 25, 2001.

FIELD OF THE INVENTION

The present invention relates to the dispensing of liquids in themicro-liter range and below and more particularly to a system and methodfor transferring liquids at accurately controlled rates and volumethrough the use of independent precision rotary and linear motionmechanisms.

BACKGROUND OF THE INVENTION

Precision liquid dispensing systems have been successfully employed inmany applications where safe and accurate handling of fluids isrequired. Precision liquid delivery is an important function in theproduction and research of many products, especially for the medical andpharmaceutical industries. Ease of use and reliability, combined withaccuracy, are extremely important in the successful performance of eachapplication.

There are several main technologies which are commonly used indispensing fluids in the micro-liter range. These include piston pumps,peristaltic pumps, time pressure systems, diaphragm pumps and gearpumps. Each of these technologies must incorporate some sort of valvingtechnology along with a method for displacing fluid. It is generallyunderstood that, in order to achieve accurate and reliable dispenses,positive displacement mechanisms have exhibited the best performance.Most positive displacement mechanisms incorporate out of phase checkvalves and a piston or other positive displacement mechanism to createsuction and discharge.

Rotary reciprocating pumps are also commonly used in the industry inorder to accomplish small volume dispensing. Rotary reciprocating pumpsutilize synchronous rotation and reciprocation of a piston in aprecisely mated cylinder bore. One pressure and one suction stroke arecompleted per cycle. A duct on the piston connects a pair of cylinderports alternatively with the pumping chamber, i.e., one port on thepressure portion of the pumping cycle and the other on the suctioncycle. A pump head module containing the piston and cylinder is mountedin a manner that permits it to be swiveled angularly with respect to therotation drive member. The degree of angle controls stroke length and inturn flow rate. The direction of the angle controls flow direction. Thistype of pump has been found to perform accurate transfers of bothgaseous and liquid fluids. A typical rotary reciprocating pump is shownin U.S. Pat. No. 4,008,003 to Pinkerton.

A variation of the conventional rotary reciprocating pump is disclosedin U.S. Pat. No. 5,312,233 to Tanny et al. Tanny et al. disclose arotary/reciprocating liquid dispensing pump having a piston selectivelypositioned in alignment with one of a plurality of circumferentiallyspaced small diameter radial passages of a pump housing. Rotation of thepiston is achieved conventionally by a stepping motor. However, therotary motion of the piston is achieved by an electromagneticclutch/braking mechanism concentrically surrounding a lead screw. Thestepping motor is incrementally pulsed and the electromagneticclutch/braking mechanism energized for selective incremental rotation ofthe lead screw.

The metering pumps of the prior art suffer from several disadvantages.One disadvantage of the prior art metering pumps is that the rotationaland the linear motion of the piston are tied together. In other words,it is not possible with the prior art pumps to independently control thespeed of rotational and linear motion of the piston. This has the effectof limiting the accuracy of dispensed liquid volume that can beachieved. In some applications, where it is necessary to provideextremely precise flow rates from inflow and/or outflow ports, it ispossible to carefully adjust the angular orientation of a rotaryreciprocating pump head module to achieve the desired accuracy. However,this is a difficult hit-or-miss, trial by error procedure that is verytime consuming.

Another problem with some prior art dispensing systems is that, once thedesired volume of liquid has been dispensed, there is typically someremnant liquid left on the nozzle tip that can sometimes inadvertentlydrip. In order to prevent excess liquid from dripping from the nozzle,some prior art systems utilize a secondary valve, such as a solenoidvalve or a diaphragm valve, to draw back any remnant fluid back into thenozzle. However, a problem with these secondary valves is the added costand complexity to the system. Additionally, a secondary valve canfurther add to maintenance, leakage and air bubble problems. Air bubblesin the system obviously decreases accuracy in the dispensed liquidvolume.

Additionally, in some applications where, for example, a suspension isto be pumped, it is often desirable to continuously agitate thesuspension. This is conventionally accomplished through shaking orstirring means. Again, providing a system with a means to shake or stirliquid during idle dispensing periods not only adds cost and complexityto the system, but can also have detrimental effects such as theintroduction of air bubbles to the system. Furthermore, suchconventional systems only provide mixing in the external reservoirs anddo not provide for mixing within the fluid path.

Finally, conventional system designs are typically large because they donot include multiple pistons in a single housing. As a result, longerand more complex tubing runs are typically provided. When deliveringsmall volumes of liquid, it is desirable to minimize the total fluidpath and priming volumes.

Accordingly, it would be desirable to provide a system that addressesthese drawbacks of the prior art metering pumps. In particular, it wouldbe desirable to separate control of the rotational and linear motions ofthe pump piston so that any sequencing of piston rotation and linearmovement can be achieved. By separating control of rotary and linearpiston motions, increased dosage volume accuracies can be accomplishedand any variety of operating methods appropriate for different fluidproperties can be implemented.

SUMMARY OF THE INVENTION

The present invention is a system and method for transferringmicro-amounts of liquids at accurately controlled rates and volumethrough the use of independent precision rotary and linear motionmechanisms. The system generally includes a pump module, an indexingmodule for incrementally translating at least one nozzle mounted theretoand a programmable controller for controlling the pump module and theindexing module.

The pump module generally includes a chambered block, a piston driveassembly having a piston, a first motor mechanically coupled to thepiston drive assembly for rotating the piston and a second motormechanically coupled to the piston drive assembly for axiallytranslating the piston. The chambered block has a liquid chamber, aninlet port in fluid communication with the liquid chamber and adischarge port in fluid communication with the liquid chamber. The inletport of the chambered block is radially spaced from the discharge port.The piston is rotatably and translationally supported in the liquidchamber of the chambered block and includes a relieved portion. Thefirst motor rotates the piston between a first position wherein therelieved portion of the piston is aligned with the inlet port of thechambered block and a second position wherein the relieved portion ofthe piston is aligned with the discharge port of the chambered block.The second motor axially translates the piston within the liquid chamberof the chambered block independent of the first motor to alternatelydraw in and discharge liquid to and from the liquid chamber.

In a preferred embodiment, the piston drive assembly further includes adrive shaft having opposed ends and a drive shaft coupling. The pistonis connected and axially aligned with one end of the drive shaft and thedrive shaft coupling is connected with the opposite end of the driveshaft. The drive shaft coupling is rotatable together with the driveshaft, but permits axial translation of the drive shaft with respect tothe coupling. The first motor is mechanically connected to the couplingand the second motor is mechanically connected to the drive shaft.

Preferably, the pump module further includes a translating blockconnected to the drive shaft of the piston drive assembly and a leadscrew coupled to the second motor and rotatably connected to thetranslating block. The translating block permits rotation of the driveshaft with respect to the block, but axially translates the drive shaftas the lead screw rotates within the translating block.

In a preferred embodiment, the translating block is connected to thepiston drive assembly to permit axial translation of the piston withrespect to the translating block. The pump module further includes aspring connected between the piston and the translating block forproviding a biasing force against the axial translation of the pistonwith respect to the translating block.

One way of permitting axial translation of the piston with respect tothe translating block is to fix the piston to the drive shaft and permitthe drive shaft to axially translate with respect to the translatingblock. The piston drive assembly is provided with a piston couplingconnected between the piston and the drive shaft to fix the piston tothe drive shaft. The spring is disposed around the said drive shaft andcaptured between the piston coupling and the translating block. Thus,when the translating block moves, the force of the spring causes thepiston coupling to move.

Alternatively, the translating block is axially fixed to the pistondrive shaft and the piston drive assembly includes a piston couplingconnected between the piston and the drive shaft that permits axialtranslation of the piston with respect to the drive shaft. Again, thespring is disposed around the drive shaft and captured between thepiston coupling and the translating block to bias the axial translationof the piston.

In still another alternative embodiment, the drive shaft of the pistondrive assembly includes an axial bore having a bottom wall and thepiston is disposed in the axial bore to permit axial translation of thepiston with respect to the drive shaft. The spring is captured withinthe bore between the piston and the bottom wall. In this embodiment, thetranslating block is axially fixed to the drive shaft.

In yet another alternative embodiment, the piston drive assemblyincludes a piston coupling connected between the piston and the driveshaft and a spacer disposed around the drive shaft between the pistoncoupling and the translating block. The piston coupling permits axialtranslation of the piston with respect to the piston coupling. The driveshaft includes an axial bore and the spring is captured within the boreto provide a biasing force against the axial translation of the piston.The spacer axially fixes the translating block to the drive shaft of thepiston drive assembly.

In further preferred embodiments, the relieved portion of the piston isa longitudinal groove. The longitudinal groove includes a bottom wall, arear wall, two side walls and fully radiussed transition surfacesbetween all the walls. The chambered block preferably includes atemperature control means disposed therein for regulating thetemperature of a liquid in the chambered block. The chambered blockfurther preferably includes a reservoir connected to the inlet port forsupplying a liquid to the liquid chamber and a tube connected at one endto the discharge port and having a nozzle connected at an opposite endthereof for dispensing a liquid from the chambered block.

The pump module can include only one piston drive assembly or aplurality of piston drive assemblies. Where more than one piston driveassembly is utilized, the translating block is connected to each driveshaft of the piston drive assemblies for simultaneously axiallytranslating the drive shafts. The first motor is then mechanicallylinked to each coupling of the piston drive assemblies forsimultaneously rotating the drive shafts.

The present invention further includes a piston coupling for amicro-liter range liquid dispensing system for connecting a piston to apiston drive shaft. The piston coupling includes a U-shaped body portionhaving a U-shaped arm and an annular barrel-shaped bearing seated in theU-shaped body portion and retained by the U-shaped arm. The bearing hasan axial bore for receiving the piston and is designed for balancing theforces applied to the piston by the piston drive shaft directly on thecenterline of the piston. Preferably, the annular barrel-shaped bearingincludes a pin for connecting the piston to the bearing and forconnecting the bearing to the U-shaped body portion. The pin extendstransversely through the bearing and is sized to be press-fit into thebearing and slip-fit into the U-shaped body portion for easy mountingand removal of the piston to and from the coupling.

The present invention also involves a method for pumping a liquidthrough a chambered block having a liquid chamber, an inlet port influid communication with the liquid chamber and a discharge port influid communication with the liquid chamber, wherein the inlet port isradially spaced from the discharge port. The method includes the stepsof: rotating a piston within the liquid chamber until a relieved portionof the piston is aligned with the inlet port; axially retracting thepiston until a desired volume of liquid is drawn into the liquid chamberfrom the inlet port; rotating the piston so that the piston closes boththe inlet port and the discharge port; applying pressure to the liquidin the liquid chamber with the piston; absorbing the force of theapplied pressure with a spring; rotating the piston until the relievedportion of the piston is aligned with the discharge port; and releasingthe force absorbed by the spring whereby the spring drives the pistonforward into said liquid chamber.

Another method, according to the present invention, for pumping a liquidthrough a chambered block having a liquid chamber, an inlet port influid communication with the liquid chamber and a discharge port influid communication with the liquid chamber, wherein the inlet port isradially spaced from the discharge port, includes the steps of: rotatinga piston within the liquid chamber until a relieved portion of thepiston is aligned with the inlet port; axially retracting the pistonuntil a desired volume of liquid is drawn into the liquid chamber fromthe inlet port; rotating the piston until the relieved portion of thepiston is aligned with the discharge port; axially translating thepiston forward into the liquid chamber while the relieved portion isaligned with the discharge port until a desired volume of liquid isdischarged from the liquid chamber into the discharge port; and brieflyretracting the piston at the end of its forward translation to reversefluid pressure applied at the discharge port.

The present invention further involves a method for maintaining fluidmotion of a liquid being pumped through a chambered block having aliquid chamber, an inlet port in fluid communication with the liquidchamber and a discharge port in fluid communication with the liquidchamber, wherein the inlet port is radially spaced from the dischargeport. The method includes the steps of rotating a piston within theliquid chamber until a relieved portion of the piston is aligned withthe inlet port and alternately retracting and inserting the piston inthe liquid chamber while the relieved portion is aligned with the inletport to alternately draw in and discharge liquid through the inlet portto maintain fluid motion during idle pumping periods.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed as an illustration only and not as a definition ofthe limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the reagent addition system formed inaccordance with the present invention.

FIG. 2 is a top view of the internal components of the pump module shownin FIG. 1.

FIG. 3 is a side view of the internal components of the pump moduleshown in FIG. 1.

FIG. 4 is a top perspective view of the pump module showing an isolatedpiston drive assembly.

FIG. 5 is a top perspective view of an alternative embodiment of thepump module showing an isolated piston drive assembly.

FIG. 6 is a top perspective view of another alternative embodiment ofthe pump module showing an isolated piston drive assembly.

FIG. 7 is a top view of one of the pistons of the piston drive assembly.

FIG. 8 is a side cross-sectional view of the piston shown in FIG. 7taken along the line 8-8.

FIG. 9 is an end cross-sectional view of the piston shown in FIG. 8taken along the line 9-9.

FIG. 10 is a cross-sectional view of the chambered block showing thepiston being retracted to intake fluid.

FIG. 11 is a cross-sectional view of the chambered block showing thepiston being driven forward to discharge fluid.

FIG. 12 is a top perspective view of an alternative embodiment of apiston coupling.

FIG. 13 is a side view of the piston coupling shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the system 10 according to the presentinvention generally includes four component modules: the nozzle indexingmodule 12; the control interface 14; the control cabinet 16; and thepump module 18.

The nozzle indexing module 12 is the unit on which a plate 20 is placedto be filled. The plate 20 includes a plurality of fluid wells 22arranged in a series of rows for receiving the dispensed fluid from thesystem 10. The plate 20 shown in FIG. 1 includes 96 fluid wells 22,however, a variety of well arrays can be addressed with the presentinvention. The nozzle indexing module 12 is a conventional unit andincludes the automated mechanisms (not shown) to step-wise position thenozzles 24 of the pump module 18 over the successive rows of wells 22 ofthe plate 20. It is available with the motion control features requiredto fill multi-well plates 20. Typically, the nozzle indexing module 12includes a stepper motor for incrementally translating one or morepistons 26. The pistons 26 are connected to a mounting plate 28 to whichthe nozzles 24 of the pump module 18 are mounted. The nozzle indexingmodule 12 may further include a priming tray 30 for draining fluids. Thepriming tray 30 is used upon start-up of the system to prime the nozzles24 and upon completion of the filling procedure to drain any remainingfluid discharged from the system 10.

The control interface 14 is preferably a standard manual keypad whichallows operator interface with the system 10. The control interface 14can also be a PC interface. The control interface 14 is used by theoperator to program and control the system 10 and can also be used formanual interruption or adjustment to system operation.

The control interface 14 is in electrical communication with the controlcabinet 16, which contains the hardware for operating the system. Thecontrol cabinet 16 is typically a stainless steel cabinet placed ormounted near the indexing module 12 and the pump module 18. There arethree signal cables (not shown) and one power cable (not shown) comingfrom the control cabinet 16. One signal cable is electrically connectedto the pump module 18, another is connected to the nozzle indexingmodule 12 and the third is connected to the control interface 14.

The pump module 18, which will be discussed in further detail below, ismounted or otherwise positioned adjacent the nozzle indexing module 12and the control cabinet 16. The pump module 18 is preferably positionedabove the nozzle indexing module 12 and may include legs 32 straddlingthe indexing module, as shown in FIG. 1. The pump module 18 includes atleast one reservoir 34 connected to the pump module in a verticalorientation for supplying a fluid to the pump module. Preferably, thepump module 18 includes a plurality of individual reservoirs 34 arrangedin a line, as shown in FIG. 1. For standard 96 and 384 fluid well trays,eight reservoirs 34 work effectively. Each reservoir 34 is connected toa chambered block 36 and is in fluid communication with a respectivenozzle 24 via tubing 38. As mentioned above, the nozzles 24 are mountedon the indexing module mounting bracket 28 for translating therewith.Thus, fluid from the reservoirs 34 is pumped through the chambered block36 and is dispensed through the nozzles 24 into the tray 22.

Each reservoir 34 is driven by a piston drive assembly 42 containedwithin a housing 40 of the pump module 18. FIGS. 2 and 3 show top andside elevation views of the internal pump components of the pump module18 within the housing 40. FIGS. 2 and 3 show eight piston driveassemblies 42 arranged in a side by side relationship, however, thenumber and arrangement of the piston drive assemblies may vary. Indeed,it is conceivable that the pump module can include only a single pistondrive assembly 42, as shown in FIG. 4, with an associated reservoir 34and nozzle 24.

Referring to FIGS. 2-4, each piston drive assembly 42 generally includesa pump piston 44, a piston drive shaft 46 and a piston drive shaftcoupling 48. The pump piston 44 is connected to one end of the pistondrive shaft 46 and is axially aligned with the drive shaft. The pumppiston 44 can be connected to the drive shaft 46 via a piston coupling50 in the form of an angled bracket as shown in FIGS. 2-4. One leg ofthe piston coupling drive bracket 50 is pinned to the pump piston 44 bya pin 52, which may be a pin bearing. The other leg of the pistoncoupling drive bracket 50 is connected to the piston drive shaft 46 by apin 54 so that the piston 44 is axially aligned with the drive shaft.The piston coupling 50 enables the use of commercially availablemetering pump pistons that can easily be connected and disconnected tothe piston coupling. Alternatively, the pump piston 44 can be connecteddirectly to the piston drive shaft 46.

At its opposite end, the piston drive shaft 46 is connected to thepiston drive shaft coupling 48. This connection is achieved by a pin 58and slot 60 arrangement whereby the piston drive shaft can axiallytranslate with respect to the coupling. Thus, the piston drive shaft 46includes a pin 58 that translates in a slot 60 formed in a couplingportion 62 of the coupling 48, or vice versa. The coupling 48 furtherincludes a pulley portion 64 formed on the opposite end of the couplingportion 62. The coupling 48 is rotatably supported in a stationarysupport block 66 such that the coupling portion 62 extends from one faceof the block and the pulley portion 64 extends from the opposite face.The coupling 48 can rotate with respect to the block 66, but is axiallyfixed to the block by retaining bearings 68.

The drive shaft 46 is further rotatably supported in a translating block70 connected to the piston drive assembly 42 between the coupling 48 andthe piston coupling 50. The translating block 70 includes a drive shaftdisplacement bearing 72 that permits rotation of the drive shaft withrespect to the translating block. The translating block 70 is connectedto the piston drive assembly 42 in such a manner that translation of thetranslating block translates the piston 44. This is most simply achievedby axially fixing the translating block 70 to the piston drive shaft 46.The translating block 70 is further connected to a lead screw 76 fordriving the piston drive shaft 46 in an axial direction. The translatingblock 70 includes a bracket 78 having a lead screw nut 80 through whichthe lead screw 76 is threaded. Thus, as the lead screw 76 rotates, thelead screw nut 80, along with the translating block 70, travels alongthe length of the lead screw. Because the translating block 70 is fixedalong the axis of the piston drive shaft 46, the piston drive shafttraverses in the axial direction along with the translating block.

Preferably, however, the translating block 70 is connected to the pistondrive assembly 42 to permit axial translation of the piston 44 withrespect to the translating block. (The purpose of this arrangement willbe discussed in further detail below.) Thus, the translating block 70can be made to permit axial translation of the piston drive shaft 46therethrough. To axially drive the piston 44, the piston drive assembly42 includes a spring 74 connected between the piston 44 and thetranslating block 70 for providing a biasing force against the axialtranslation of the piston with respect to the translating block. Thespring 74 can be captured around the drive shaft 46 between thetranslating block 70 and the piston coupling 50. The spring 74 providesa biasing force against rearward (i.e., toward the coupling 48) axialtranslation of the piston coupling 50 with respect to the drive shaft46. Thus, when the translating block 70 moves, the force of the spring74 causes the piston 44 to move.

Another way of permitting axial translation of the piston 44 withrespect to the translating block 70 is to fix the translating block tothe piston drive shaft and make the piston axially translatable withrespect to the drive shaft 46. In this embodiment, the drive shaftdisplacement bearing 72 prevents the drive shaft 46 from axiallytranslating with respect to the translating block 70. The pistoncoupling 50 is connected to the drive shaft 46 by a pin 54 and slot 56arrangement, as shown in FIG. 3, whereby the piston coupling, and thusthe piston 44, can translate a small distance axially with respect tothe drive shaft. The pin 54 can be fixed within the bracket 50 andtranslate within a slot 56 formed on the drive shaft 46, or vice versa.

In still another alternative embodiment, as shown in FIG. 5, the driveshaft 46 of the piston drive assembly 42 includes an axial bore 73having a bottom wall 75 and the piston 44 is disposed in the axial boreto permit axial translation of the piston with respect to the driveshaft. The piston 44 can include a pin 77 which traverses in a slot 79formed in the drive shaft 46 to permit axial translation of the pistonwith respect to the drive shaft. A spring 81 is captured within the bore73 between the piston 44 and the bottom wall 75. In this embodiment, thetranslating block 70 is axially fixed to the drive shaft 46, for exampleby the retaining bearing 72.

In yet another alternative embodiment, as shown in FIG. 6, the pistondrive assembly 42 includes a piston coupling 50 connected between thepiston 44 and the drive shaft 46 and a spacer 83 disposed around thedrive shaft between the piston coupling and the translating block 70.The piston coupling 50 permits axial translation of the piston 44 withrespect to the piston coupling. This can be achieved by providing a slot85 in the coupling 50 in which the piston pin 52 translates. The driveshaft 46 includes an axial bore 87 and a spring 89 is captured withinthe bore to provide a biasing force against the axial translation of thepiston 44. The spacer 83 is captured between the piston coupling 50 andthe translating block 70 to axially fix the translating block to thedrive shaft 46 of the piston drive assembly 42.

Rotation and axial translation of the pump piston 44 are driven by twoindependent rotary motors 82 and 84. The motors 82 and 84 are alsocontained within the housing 40 of the pump module 18 along with thepiston drive assemblies 42. The motors 82 and 84 are electricallydriven, stepping or servo, or pneumatically driven. One motor 82 servesto control rotation of the pump piston(s) 44, while the other motor 84serves to control linear displacement of the piston(s). The first motor82 controlling piston rotation is connected on its output shaft 86 tothe pulley portion 64 of the piston drive shaft coupling 48. A timingbelt 88 connected between the first motor 82 and the coupling 48 isshown in the drawings, however, other mechanical linkages, such as arack and pinion, can be utilized. Rotation of the coupling 48 in turnrotates the piston drive shaft 46. The second motor 84 controllinglinear displacement of the pump piston 44 is coupled to the lead screw76 by a coupling 90. Rotation of the coupling 90 in turn rotates thelead screw 76. As described above, rotation of the lead screw 76displaces the lead screw nut 80, which is connected to the translatingblock 70, which in turn axially translates the pistons 44.

Referring now to FIGS. 7-9, the pump piston 44 is a cylindrical memberhaving a shoulder portion 92, which is secured to the piston coupling50, and a fluid dispensing portion 94, which is seated in close slidingrelationship within the chambered block 36. The fluid dispensing portion94 is preferably made from a ceramic material and is press-fit orotherwise fixed to and axially aligned with the shoulder portion 92. Thefluid dispensing portion 94 of the piston 44 includes a relieved portion96 designed to direct fluid into and out of the chambered block 36.Preferably, the relieved portion 96 takes the form of a narrow grooveformed parallel to the axis of the piston 44. More preferably, thegroove 96 includes a fully radiussed transition surface 96a between thebottom 91 and the rear wall 93 of the groove and fully radiussedtransition surfaces 96b between the bottom 91 and the side walls 95 ofthe groove so as to avoid sharp edges within the groove. This minimizesthe attachment of air bubbles or fluid components to any surfaces andallows for bubble clearing, which is desirable when transferringmicro-amounts of liquid accurately. Additionally, where the groove 96meets the outer diameter of the piston 44, a sharp edge 97 is preferablyprovided. In other words, the transition between the groove 96 and theouter surface of the piston 44 is not radiussed, thereby leaving a sharpedge 97 at the transition. The sharp edge 97 is utilized to scrape theinner walls of the liquid chamber 98 of the chambered block 36 as thepiston 44 rotates within the chamber to clean the walls during use orduring a cleaning cycle. The depth and length of the relieved portion 96of the piston 44 may be chosen depending on pump size and dose volumerange required. Though not preferred, the relieved portion 96 may takeother forms, such as a flat.

FIGS. 10 and 11 illustrate operation of the piston 44 within thechambered block 36. As mentioned above, the fluid dispensing portion 94of the piston 44 is seated in close sliding relationship within a fluidchamber 98 formed in the chambered block 36. The piston 44 and/or thechambered block 36 may include O-rings (not shown) to ensure afluid-tight seal therebetween. FIGS. 10 and 11 further show a fluidreservoir 22 connected to an inlet port 100 of the chambered block 36and tubing 38 connected to a discharge port 102 of the chambered block.The inlet port 100 and the outlet port 102 are radially spaced and arein fluid communication with the fluid chamber 98. In certainapplications, only one inlet/outlet port is required. In otherapplications, a plurality of radially spaced inlet/outlet ports can beprovided in the chambered block 36. The reservoir 22 and tubing 38 canbe connected to their respective ports by conventional fluid-tightfittings 104. The present invention could also be used to pump fluidfrom remote reservoirs, wherein intake tubing would be connected to theinput port 100 in place of the reservoir 22.

Fluid displacement through the chambered block 36 is achieved by variouscombinations of rotary and linear motions of the piston 44. In order todraw fluid into the fluid chamber 98 from the reservoir 22, the piston44 is rotated as required to align the relieved portion 96 with theintake port 100. The piston 44 is then drawn back as required to take inthe desired volume of fluid into the chamber 98. Withdrawal of thepiston 44 produces a negative pressure within the chamber 98, whichdraws in fluid from the reservoir 22. The piston 44 is then rotated toalign the relieved portion 96 with the discharge port 102 of thechambered block 36. Finally, the piston 44 is driven forward therequired distance to force fluid into the discharge port 102 and out ofthe chambered block 36 via the tubing 38 to produce the desireddischarge dose. Again, rotation and translation of the piston 44 iscontrolled by the individual motors 82 and 84 of the pump module 18.

The chambered block 36 further preferably includes at least onetransverse bore 106 formed therein and extending perpendicularly to thefluid chamber 98. The bore 106 can be any shape. A temperature controlmeans 108, 110 is disposed within the bore 106 for regulating thetemperature of a liquid flowing through the chambered block 36. Thetemperature control means can be a conventional cylindrical cartridgetype heating element 108 or cooling element 110 that is inserted withinthe bore 106 to heat or cool the fluid being pumped through thechambered block 36. FIGS. 10 and 11 show a heating element 108 insertedin an upper bore 106 a and a cooling element 110 inserted in a lowerbore 106 b of the chambered block 36. The heating and cooling elements1108 and 110 can be electrically connected to the control cabinet 16 forheating or cooling the fluid as desired. Alternatively, the temperaturecontrol means 108, 110 can take the form of heat exchangers, wherein aheated or cooled liquid is pumped through the bores 106 to transfer orwithdraw heat to or from the chamber fluid. This feature provides theability to control fluid temperature throughout the fluid path.

FIGS. 12 and 13 show an alternative embodiment of a piston coupling 112used to connect the piston 44 to the piston drive shaft 46. The pistoncoupling 112 includes a U-shaped body portion 114 having a U-shaped arm116. Seated in the U-shaped body portion 114 and retained by theU-shaped arm 116 is an annular barrel-shaped bearing 118. The bearing118 includes an axial bore 120 for receiving the piston 44. The bearingfurther includes a bore 121 for receiving a pin 122 for connecting thepiston to the bearing. The pin 122 extends transversely through thebearing 118 and is preferably sized to be press-fit into the piston 44and the bearing 118. The coupling body portion 114 includes a slot 124for receiving the pin 122 and thereby driving rotation of the piston viathe pin. The pin 122 is preferably slip-fit into the slot 124 of thebody portion 114. The reason for the slip-fit clearances of the pin 122is to account for any angular misalignment between the piston driveshaft 46 and the liquid chamber 98 of the chambered block 36. It alsoprovides for simple and effortless mounting and removal of the piston 44from the coupling 112. The annular barrel-shaped bearing 118 is sodesigned to balance the forces applied to the piston 44 by the pistondrive shaft 46 symmetrically about the centerline of the piston. Priorart coupling designs tend to apply force on the piston in a manner thatcreates a moment about the piston. This moment can result in stresses onthe piston, which in turn can lead to piston failure.

Returning to FIGS. 3-6, an additional feature of the present inventionthus far described is the use of spring loaded “lost motion” to enablerapid yet accurate piston displacement so as to increase fluid dischargevelocity. “Lost motion” in mechanical devices refers to providing forone portion of a mechanical linkage being in motion while anotherportion pauses or dwells in one position before resuming motion. In thiscase, “lost motion” is used to drive the translating block 70 forwardwhile the relieved portion 96 of the pump piston 44 is not aligned withthe discharge port 102. Back pressure from the closed discharge port 102within the fluid chamber 98 will momentarily prevent the piston 44 frommoving forward. Because the piston drive assemblies 42 in all theembodiments described above are designed to permit slight axialtranslation of the piston 44 with respect to the translating block 70,the spring 74, 81 or 89 located between the piston and the translatingblock absorbs the force applied by the translating block being drivenforward. Once the relieved portion 96 of the piston 44 is aligned withthe discharge port 102, the spring 74, 81 or 89 drives the pistonforward at a high speed to achieve faster discharge of fluid but stillthe correct metered amount. This rapid delivery enables proper cut offof very small doses from the dispense tips. Alternatively, this effectcan be achieved with larger, high torque motors and appropriate drivecontrols and circuitry.

The above described design separates control of rotary and linear pistonmotions so as to enable a variety of operating methods appropriate fordifferent fluid properties and dosage volumes. The various methods ofoperating the two motors 82 and 84 to achieve the above describedresults are user programmable via the control interface 14 to thecontrol cabinet 16. Alternatively, a PC with dedicated software can beused to interface with the same cabinet.

As a result of the present invention, various advantages are achieved.The system provides alternatives in sequencing rotary and linear pistonmotions so as to have a single intake for multiple doses. Additionally,the system provides for briefly reversing piston direction at the end ofeach dose so as to “kick off” drops at dispense tips. In other words, asthe piston 44 is driven forward to dispense fluid, as shown in FIG. 11,the translational motor 84 can be programmed to rapidly and brieflyreverse direction so that the piston 44 is quickly retracted a shortdistance. This action of the piston essentially removes any fluid dripsfrom the dispensing nozzles 24. As described above, the system furtherallows for building pressure in the pump chamber 98 prior to aligningthe piston 44 with the discharge port 102 so as to increase fluidvelocity and better kick off small fluid droplets. The systemadditionally allows for keeping fluid in motion during idle periodswithout dispensing so as to maintain a mixed state of fluid components.This is achieved by aligning the relieved portion 96 of the piston 44with the intake port 100 and continuously cycling the piston forward andbackward within the chambered block chamber 98 until it is time todispense. The forward and backward action of the piston will alternatelydraw in fluid from the reservoir 22 and discharge fluid into thereservoir through the intake port 100. The system further provides avery compact arrangement of multiple fluid paths so as to greatly reducefluid path priming volume and provides for easy maintenance.

For most solutions, dispense volume CV's of 1% or below for doses downto 5 μl and 3% or below down to 1 μl doses can be achieved with thepresent invention. Indeed, it has been found that doses as low as 0.1 μlare being achieved using this system. Thus, nozzle dispense tip orificesof 0.0015 diameter can be used as compared to prior art diameters of0.006-0.008. Various pump module designs are conceivable to suitdifferent fill patterns and volume range requirements. They are designedfor quick changeover allowing for multiple uses of the same basicsystem. Piston drive assemblies can be arranged to fill all wells withthe same reagent or to put different reagents into specific wells.System speed will depend on how many piston drive assemblies are used.

While there has been described what is presently believed to be thepreferred embodiments of the invention, those skilled in the art willrealize that various changes and modifications may be made to theinvention without departing from the spirit of the invention and it isintended to claim all such changes and modifications as found in thescope of the invention.

1. A piston coupling for a micro-liter range liquid dispensing systemfor connecting a piston to a piston drive shaft, the couplingcomprising: a U-shaped body portion having a U-shaped arm; and anannular barrel-shaped bearing seated in the U-shaped body portion andretained by the U-shaped arm, said bearing including an axial bore forreceiving the piston, wherein said annular barrel-shaped bearing isdesigned for balancing the forces applied to the piston by the pistondrive shaft symmetrically about the centerline of the piston, andwherein said annular barrel-shaped bearing includes an enlargedmid-section, wherein said bearing is pivotable within said U-shaped bodyportion for permitting any angular misalignment between the piston driveshaft and the piston.
 2. The piston coupling as defined in claim 1,wherein said annular barrel-shaped bearing includes a pin for connectingthe piston to said bearing and for connecting said bearing to saidU-shaped body portion, said pin extending transversely through saidbearing and being sized to be slip-fit into said U-shaped body portion.3. A piston coupling for a micro-liter range liquid dispensing systemfor connecting a piston to a piston drive shaft, the couplingcomprising: a U-shaped body portion having a U-shaped arm; and anannular barrel-shaped bearing seated in the U-shaped body portion andretained by the U-shaped arm, said bearing including an axial bore forreceiving the piston, wherein said annular barrel-shaped bearing isdesigned for balancing the forces applied to the piston by the pistondrive shaft symmetrically about the centerline of the piston and,wherein said U-shaped body portion includes a bore for receiving apiston drive shaft, said body portion bore defining a piston drive shaftaxis, and wherein said bearing axial bore defines a piston axis, andwherein said barrel-shaped bearing is pivotable within said U-shapedbody portion for permitting angular misalignment between said pistondrive shaft axis and said piston axis.
 4. The piston coupling as definedin claim 3, wherein said annular barrel-shaped bearing includes a pinfor connecting the piston to said bearing and for connecting saidbearing to said U-shaped body portion, said pin extending transverselythrough said bearing and being sized to be slip-fit into said U-shapedbody portion.